1. Field of the Invention
This invention relates generally to downhole tools for use in oil and gas wellbores and methods of anchoring such apparatuses within the casing of the wellbore. This invention particularly relates to improving the engagement of the slip elements within a casing or tubing. These slip elements are commonly used in setting or anchoring of a downhole drillable packer, bridge plug and frac plug tools.
2. Description of Related Art
In drilling or reworking oil wells, many varieties of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well by pumping cement or other slurry down the tubing, and forcing the slurry around the annulus of the tubing or out into a formation. It then becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well, or for otherwise isolating specific zones in a well. Downhole tools referred to as packers, bridge plugs and frac plugs are designed for these general purposes, and are well known in the art of producing oil and gas.
Both packers and bridge plugs are used to isolate the portion of the well below the packer or bridge plug from the portion of the well thereabove. Accordingly, packers and bridge plugs may experience a high differential pressure, and must be capable of withstanding the pressure so that the packer or bridge plug seals the well, and does not move in the well after being set.
Packers and bridge plugs used with a downhole tool both make use of metallic or non-metallic slip assemblies, or slips, that are initially retained in close proximity to a mandrel. These packers and bridge plugs are forced outwardly away from the mandrel upon the downhole tool being set to engage a casing previously installed within an open wellbore. Upon positioning the downhole tool at the desired depth, or position, a setting tool or other means of exerting force, or loading, upon the downhole tool forces the slips to expand radially outward against the inside of the casing to anchor the packer, or bridge plug, so that the downhole tool will not move relative to the casing. Once set, additional force, in the form of increased hydraulic pressure, is commonly applied to further set the downhole tool. Unfortunately, the increased pressure commonly causes the downhole tool to slip up or down the casing.
To prevent slipping of the downhole tool, cylindrically shaped inserts, or buttons, are secured to the slip segments to enhance the ability of the slip segments to engage the well casing. The buttons must be of sufficient hardness to be able to partially penetrate, or bite into the surface of the well casing, which is typically steel. Unfortunately, the buttons will occasionally disintegrate under increased force, or higher pressures, thereby allowing the downhole tool to slide within the well.
Alternatively, the slip segments may have a plurality of wickers positioned about them to engage and secure the slip segments within the casing. The wickers must be sufficiently hard to engage and deformably cut into the well casing. Unfortunately, the amount of force required to cause the plurality of wickers to engage the well casing is significant, and often exceeds that of a setting tool. Thus, until sufficient force is exerted upon the wickers, the wickers may not fully engage the casing, thereby allowing the tool to slide significant distances within the well prior to engaging the casing.